So far as is known, most, if not all, strike plates heretofore used as part of the security hardware in sliding glass door and window installations have been of the vertically-elongated metal plate type mounted on the outer face of the lock jamb by a pair of screws located near the top and the bottom of the plate and in a median vertical plane.
The vertical central plane in which the two screws are located passes through the customary central aperture in the strike plate, the aperture being positioned so as to register with the usual L-shaped latch hook as the hook moves through the aperture just prior to or just subsequent to engagement between the hook and the back face of the strike plate. When the vertical limb of the hook projects upwardly from the horizontal limb, the vertical limb lies in back of the portion of the strike plate above the central aperture when the latch hook is raised into locked position. Thus, when the door or window is urged toward open position without disengaging, i.e. lowering the latch hook, the upstanding limb of the hook abuts the back face of the strike plate and resists movement of the door or window in an opening direction.
Strike plates in which the two mounting screws are located in a median vertical plane, as just described, provide adequate resistance against moderate forces tending to pry the lock stile of the door or window away from the lock jamb of the installation. However, under the stresses exerted by forceful pry bar or large screwdriver efforts, the previous installations leave much to be desired. The upstanding limb of the latch hook exerts a strong outward force on the adjacent back face of the strike plate and tends to bend outwardly the upper portion of the strike plate. Bending often takes place about a horizontal axis passing through the upper one of the two screws holding the strike plate. As deformation proceeds, both the upper and lower portions of the strike plate bend outwardly even more, so that eventually the central aperture becomes vertically enlarged in size until the latch hook is no longer engaged and the door or window can be opened.
In other words, when the upstanding limb of the latch hook of a locked, sliding, glass door or window has been forcefully urged against the back side of a strike plate mounted with the screws lying in a median vertical plane, as in previous lock hardware, the edge of the hook deforms the metal in the path of the hook. Although the leading edge of the hook is not knife-sharp, it nevertheless is effective, where sufficient force is applied, to distort and bend the metal outwardly and upwardly, particularly in the vicinity of the upper margin of the central aperture of the strike plate, to such an extent that the hook is able to move through the vertically enlarged aperture and thus disengage the strike plate, allowing the sliding vent to be opened and permitting access to the interior.